Wheel force transducer or load cells for measuring forces along or moments about three orthogonal axes are known. The wheel force transducer typically is mounted between and to a vehicle spindle and a portion of a vehicle rim. The transducer measures forces and moments reacted through a wheel assembly at the spindle as the vehicle is operated.
One form of a wheel force transducer that has enjoyed substantial success and critical acclaim has been the SWIFT transducer sold by MTS Systems Corporation of Eden Prairie, Minn. and is described in detail in U.S. Pat. Nos. 5,969,268 and 6,038,933. Generally, this transducer includes a load cell body having a rigid central member, a rigid annular ring and a plurality of tubular members extending radially and joining the central member to the annular ring. A plurality of sensing circuits are mounted to the plurality of tubular members. The rigid central member is mounted to the vehicle spindle, while the annular ring is attached to the vehicle rim. An encoder measures the angular position of the load cell body allowing the forces transmitted through the radial tubular members to be resolved with respect to an orthogonal stationary coordinate system. An external slip ring assembly provides power to and receives signals from the sensors on the load cell body.